validator.py is a tool for ensuring that data conforms to certain sets of rules, called validations. A validation is essentially a schema for a dictionary, containing a list of rules for each key/value pair in the dictionary you want to validate. This is intended to fill a similar use case to form validations in WTForms or Rails, but for general sources of data, not just Web forms.

JS Date Range Picker is a package to let the user pick a range between two dates. It can be used to present two form inputs that let the user choose dates using calendar pull down menus. The dates may be validated so the range end date is not set to a day before the range start date. The format of the dates and the week start day are configurable parameters. The chosen dates are returned in the ISO-8601 extended format.

Android Saripaar is a simple, yet powerful rule-based UI validation library for Android. It following features declarative style validation powered by Annotations, synchronous and asynchronous validations (you don't have to worry about threading), compatibility with Stock Android Widgets, custom view dependencies, quick setup (just download the jar and include it in your libs project folder), removal of most of your validation logic from your code, and compatibility with other annotation frameworks such as AndroidAnnotations, RoboGuice, etc.,

Data Validator is a class to validate a set of values based on a list of rules. It supports the following validation orders: sequence (fields validated sequentially), all-at-once, and both (using a dependencies model). It can embed different user-defined validation rules libraries (a default built-in library is provided).

Form Validation validates form inputs according to a CSS class. It uses the jQuery library to traverse the list of inputs of a form and performs validations of types defined in a CSS class attribute of each input. It supports validations of these types: required, email, date, time currency, numeric, alphanumeric, alphabetic, state, zip code, and URL. If the fields are invalid, an error message is displayed inside a page element for displaying validation errors.

HTML::FormFu is a framework for HTML forms. It aims to be as easy as possible to use for basic Web forms, but with the power and flexibility to do anything else you might want to do (as long as it involves forms). You can configure almost any part of formfu's behavior and output. By default, formfu renders "XHTML 1.0 Strict" compliant markup, with as little extra markup as possible, but with sufficient CSS class names to allow for a wide range of output styles to be generated by changing only the CSS.

Email Address Validator is a PHP class that allows the developer to validate email addresses according to the RFC 5321 or RFC 5322 standards. It can also check to see if the domain can be resolved to MX RRs. Acceptable local-parts include dot-atom, quoted string, and obsolete. Acceptable domains include domain name, IPv4 address, IPv6 address, and IPv4-mapped IPv6 address. Folding white spaces and nested comments are also supported.

Serene is a validation engine that implements the JAXP 1.3 Validation Framework API for RELAX NG based on an algorithm centered on providing good messages and having a clear handling of ambiguity and conflicts. It has an implementation of the JAXP Validation Framework API for ISO Schematron and support for Schematron markup embedded in RELAX NG schemas.

EMF Validation Builder is an Eclipse plugin that automates the validation process at the time of saving. This means that resource problem markers are up to date as soon as you save your model. A dependency table is maintained, which allows the validation process to be re-run when necessary. In particular, the tool can be directly used with ECore model files.